Machines such as, for example, loaders, excavators, and other types of heavy equipment use multiple actuators supplied with pressurized fluid from a pump on the machine to accomplish a variety of tasks. These actuators are typically speed controlled based on an actuation position of an operator control device. For example, an operator control device such as a joystick, a pedal, or other suitable device may be movable to generate a signal indicative of a desired speed of an associated hydraulic actuator. When an operator moves the interface device, the operator expects the hydraulic actuator to move at a related speed. However, when multiple actuators are simultaneously operated, the hydraulic fluid flow from a common pump may be insufficient to move all of the actuators at their desired speeds. In these situations, the majority of the pressurized fluid from the pump flows to the actuator(s) having the least resistance, resulting in the remaining actuator(s) receiving insufficient fluid. When an actuator receives less fluid than demanded, it may move at a slower than desired speed or even stop moving completely.
One system attempting to minimize the likelihood of an actuator receiving insufficient fluid is described in U.S. Pat. No. 6,618,659 (the '659 patent) issued to Berger et al. on Sep. 9, 2003. The '659 patent describes a skid-steer loader having a first hydraulic sub-circuit associated with a boom arm, and a second hydraulic sub-circuit associated with a bucket, which is pivotally connected to an end of the boom arm. The first sub-circuit includes a boom cylinder connected to move the boom arm, and an associated electro-hydraulic boom valve that activates extension and retraction of the boom cylinder. The second sub-circuit includes an implement cylinder connected to move the bucket, and an associated electro-hydraulic implement valve that activates extension and retraction of the implement cylinder. The boom and implement valves are connected in parallel to receive a combined flow of pressurized fluid from a low flow gear pump and from a high flow gear pump. A controller is configured to receive a first input signal from a boom manual control sensor, and a second input signal from an implement manual control sensor. The controller sends a first control signal to activate the boom valve in response to receiving the first input signal, and sends a second control signal to activate the implement valve in response to receiving the second input signal. The controller is programmed to modify the second control signal in accordance with a table-based duty factor when the boom arm is lifted and the bucket is dumped simultaneously. The modified signal reduces and thereby slows down the flow of hydraulic fluid through the implement sub-circuit. As a result, more fluid is available from the low and high flow gear pumps for boom arm lift during bucket dumping than otherwise would have been available.
Although the skid-steer loader of the '659 patent may benefit from improved boom lift during a bucket dumping event, the benefit and applicability thereof may be limited. That is, although perhaps suitable for a small skid-steer type loader, the table-based duty factors described above may function poorly with another type or size of machine. In addition, the use of multiple pumps may result in complex flow control and unpredictable instabilities. Further, the use of fixed displacement gear type pumps may limit modulation of the pressurized fluid supply.
The disclosed hydraulic implement system is directed to overcoming one or more of the problems set forth above.